FALL RIVER - Placing Joseph Kennedy III on the family tree made for a political parlor game of sorts for residents here last week.

Some thought Kennedy III was Ted Kennedy’s son, others thought he was the child of Bobby Kennedy. A few wondered whether he was the “oil guy,’’ referring to Joseph Kennedy II. But even among those who figured out that he was the oil guy’s kid, virtually no one knew his first name.

“You say he’s Robert’s grandson?’’ said a puzzled Paul Kerry as he sat down at a diner booth. “Never heard of him.’’

When it comes to name recognition, Joseph Kennedy III is a political paradox. Many voters, even staunch Democrats, haven’t the faintest idea who he is. Yet everyone knows his family.

AP/File

News that a Kennedy (Joseph P. Kennedy III) was poised to run for the House seat held for decades by the retiring Barney Frank has sparked intense interest, and a reflexive support that constituents readily admitted is only name-deep.

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In Massachusetts, especially in Democratic strongholds where nostalgic affection for the Kennedys still runs deep, that pedigree remains compelling enough to vault a 31-year-old political novice into a leading Congressional contender.

In this working-class city, news that a Kennedy was poised to run for the House seat held for decades by the retiring Barney Frank has sparked intense interest, and a reflexive support that constituents readily admitted is only name-deep.

“I voted for them all, every one,’’ said Lorraine Bettencourt, 76, as she combed through the racks of a thrift store Friday. “I don’t know much about this one, but I was wishing they’d come back to politics. They seem to be smart people, the Kennedys. They do a good job.’’

Her husband, waiting patiently outside, agreed that the Kennedy name was good enough for him, especially given the current state of political affairs.

“They certainly don’t need the money,’’ he noted dryly. “So I guess they want to do the job.’’

Most political observers believe the redrawn lines of the Fourth Congressional District - from Newton to Fall River - are decidedly more favorable to Republicans, who are expected to make a strong bid for the seat this fall. But at the two ends of the hodgepodge district, Democratic mainstays who backed Frank time and again will be critical in the next election. And the lingering Kennedy mystique remains a considerable political advantage that even now seems certain to shape the field and scare off would-be political rivals.

“The Republicans are for the rich,’’ said Joseph Torres, 64, a retired construction worker, summing up the sentiment of many residents of the city’s north side. “The Kennedys are for the poor. They’ve had a lot of bad luck, but they are good people.’’

Like many here, Torres said he had never heard of this particular Kennedy.

Angelo Borges had just read about a new generation of Kennedys joining the political fray, and was heartened by the news.

“It’s good to have them back,’’ said the 62-year-old barber. “If he runs, he’s got my vote.’’

Borges said he was not worried about Kennedy’s lack of political experience, or what political views he might hold. As an independent, he had voted for Republican Sean Bielat last time around against Barney Frank, who he did not care for.

But that was different. Like his father before him, Borges has voted for Kennedys his whole life, and isn’t about to stop now.

“That’s the way it is in Massachusetts,’’ he said flatly.

Such knee-jerk Kennedy admiration, a longstanding mystery to many, frustrated other voters, who said elections should be about more than name recognition, especially given the country’s economic troubles.

“Not a fan,’’ grumbled Jeffrey Vilao, 39, as he unloaded supplies at a fruit and flower shop. “Not at all.’’

At Dunkin’ Donuts, several customers said no one would be paying any attention to a young public prosecutor if he did not have a famous name.

“I know the family,’’ said Tom Medeiros, 61. “I know nothing about him. I need a lot more information.’’

In Fall River and Newton, two vastly different cities with a shared tradition of supporting Democrats, many constituents said candidates should have to prove their own worth.

“I’ll judge him on his merits, not on his name,’’ said Barbara Gaffin, 57, Newton. “The Kennedys do not own any political seat in Massachusetts.’’

Gaffin, a supporter of Frank, said she hoped Kennedy would “follow in his tradition.’’

In Newton, residents seemed to take a wait-and-see approach toward Kennedy’s candidacy, saying that while his name gives him a clear political edge, it would not sway their vote.

But Fall River residents voiced enthusiasm at the prospect of a Kennedy in Congress, saying his family background suggested he would have their interests at heart.

“Good guys, good politics,’’ said Cheryl Servant, an out-of-work health care aide. “It’s a family thing.’’

Younger voters generally seemed less impressed by the name, and said they would vote for whomever they thought best for the job. But they agreed that while the Kennedy mystique has faded over time, its hold among older voters remains.

“It absolutely carries weight,’’ said Emily Shuster, a 20-year-old who grew up in Newton and voted for Frank in the last election. “It’s unmistakable.’’

At a laundromat in Fall River, two friends chatted about the new Kennedy on the scene. Red hair on this one, Pat Frazer noted. And a name that somehow feels like family.

“It’s in their blood,’’ said Dawn Rego, 54. “Plus you can’t do worse than the rest of them.’’